1. Field of the Invention
The present invention relates generally to a height control system for an automotive suspension system for adjusting or regulating a vehicular body height within a predetermined height range. More specifically, the invention relates to a vehicular height control system which can avoid the necessity of height adjustment upon ON-set of power supply.
2. Description of the Background Art
Various vehicular height control systems or height regulating systems have been developed and proposed. One of the known vehicle height control systems has been illustrated in the Japanese Patent First (unexamined) Publication No. 58-112817, published on July 5, 1983. In the shown vehicular height control system, relative height level of the vehicle body to suspension members are monitored and height control is performed with respect to each wheel position independently of other wheel positions. Such control is generally successful in regulating vehicular attitude.
Such height control systems are active for performing adjustment of the vehicular height while electric power supply is maintained. In order words, the suspension control system will be held inactive while the main power switch, e.g. ignition switch, is held OFF. Therefore, the vehicular height cannot be controlled while the vehicle is in a parking condition and thus the main power supply is held OFF. As will be understood, upon parking, the vehicular occupant or occupants will get off the vehicle to reduce the load on the vehicle. As a consequence, the force of the suspension system becomes excessive to rise the vehicular height across an acceptable higher vehicle height level. Since the main power supply is shut off at this vehicular height position, the vehicle may be held at extraordinary height position.
In order to avoid this, the Japanese Patent First (unexamined) Publication (Tokkai) Showa 55-47908 proposes a vehicular height control system which may perform height adjustment for a given period of time after shutting OFF the main power supply. The other vehicular height control system has been proposed in the Japanese Utility Model First Publication (Jikkai) Showa 59-121221. The disclosed system features height adjustment while the main power supply is held OFF, to adjust the height so as to maintain the vehicular height within a given normal height range when the vehicular height is higher than normal height range.
By the foregoing two prior proposed systems, vehicular height adjustment can be performed even after shutting OFF the main power supply to maintain the vehicular height within the predetermined normal height range. However, note is to be given that the height adjustment in the parking condition of the vehicle is performed under substantially no passenger's load condition. This means that the load condition at the vehicular parking position is held minimum. Since height adjustment is performed at minimum load condition, the suspension force to suspend the vehicle body on suspension systems natually becomes minimum.
At this position, when the vehicular occupant or occupants return to the vehicle and get therein, load is increased which tends to excessively lower the vehicular height level. Therefore, upon starting main power supply to make the vehicular height control system active in normal state, this lowered height position of the vehicle is sensed. As a result, height control may be performed to recover the vehicular height. This clearly degrades riding comfort.
Furthermore, since the pressure source unit including a pressurization pump, such as a compressor, is held inactive while the main power supply is OFF, substantial load may be exerted on the pressurization pump to shorten the life thereof. In addition, since the pressurization pump requires a period for raising pressure of working fluid, this period serves as a lag time in height adjustment. Therefore, it will take a relatively long period for raising the vehicular height within the normal height range.